1. Field of the Invention
The present invention is directed to an apparatus and method for removing a solvent.
2. Description of the Prior Art
The technique of forming a thin film of uniform thickness, e.g., a photoresist film, on a substrate is the knowledge of public domain. In the process of forming the thin film, a need exists to dry a coat deposited on the substrate. One known method for drying the coat is to heat up the coat as a whole.
This conventional method is, however, disadvantageous in that a solvent (liquid) contained in the coat goes rapidly vaporized from the surface of the coat, thus creating a density difference between the surface and the interior of the coat and reducing, by convection, the surface flatness of the film acquired.
Furthermore, the film thus acquired shows poor thickness distribution due to the insufficiency of flowage-caused self-leveling action. Particularly, because the drying speed at a peripheral edge of the substrate is faster than at the center thereof, the film exhibits increased thickness difference between the center part and the peripheral edge part (marginal end part). In addition, the afore-mentioned method poses a problem in that the uniformity of components in a liquid film material is decreased to thereby bring about instability in the film quality.
Another known method for drying the coat is to extinguish the flowability of the coat by baking (thermally treating) a liquid material coated on a substrate under a vacuum condition. Reference is made to, for example, JP-A No. 8-194316. In this prior art method, however, the solvent is dried abruptly at a high vacuum degree, which may unintentionally change the properties of a resist material and roughen the surface of the thin film produced.